Wide uses have been found lately for apparatus for applying coatings by gas detonation where acetylene is employed as the combustible ingredient of an explosive mixture due to high detonation capacity of acetylene-oxygen mixtures, or, otherwise stated, due to the shortest combustion-to-detonation path of all the available explosive gaseous mixtures. These advantages of acetylene-oxygen mixtures allow the use of short barrels in apparatus for applying coatings by gas detonation to result in a saving in the amount of metal consumed for the fabrication of the apparatus and a high capacity thereof.
However, the use of acetylene as the combustible compound of explosive gas mixtures is fraught with hazards, sice detonation of acetylene-oxygen mixtures tends to propagate even through clearances less than 0.1 mm; in addition, acetylene is capable of detonation in complete absence of oxygen in the mixture.
These properties of acetylene-oxygen mixtures necessitate extra arrangements to prevent the breakthrough of detonation from the barrel of the apparatus along gas passages to the acetylene manifold (backfire).
There is known a gas detonation apparatus (cf., U.S. Pat. No. 2,869,924) in which backfire is obviated by providing a protective tubular coil to be filled with an inert gas (nitrogen) prior to initiating detonation of an explosive mixture serving as an obstacle in the path of propagation of the detonation wave, and other devices are used for preventing backfire.
However, the use of such devices fails to guarantee complete safety during operation of apparatus for applying coatings by gas detonation employing acetylene-oxygen mixtures. Safety can be ensured only through the use of hard-to-detonate explosives as O.sub.2 + methane, propane, butane and the like. An accompanying disadvantage resides in that the use of hard-to-detonate mixtures necessitates longer barrels than those in apparatus operating on acetylene-oxygen mixtures due to a substantial elongation of combustion-to-detonation path during formation of a detonation wave in the barrel and, as a consequence, resulting in a higher consumption of gas and reduced capacity of the apparatus through reducing the number of shots per second.
With respect to hard-to-detonate mixtures the combustion-to-detonation path exceeds 100 times the length of such a path in acetylene-oxygen mixtures.
In order to make use in apparatus for applying coatings by gas detonation of hard-to-detonate mixtures without increasing the size of the apparatus, while maintaining the output capacity and consumtpion of working gases, it is necessary to provide in the barrels special arrangements reducing the combustion-to-detonation path.
There is also known a barrel of a detonation apparatus having a coil at the walls thereof (cf. K. I. Schelkin and Y. L. Troshin "Gazodinamika gorenia", 1963, AN SSSR Publishers, Moscow, page 206) where propagation of the flame is accelerated through additional agitation thereof during interaction of the gas flow with obstacles, such as the coil turns. However, the use of the Schelkin coil in initiating hard-to-detonate mixtures affords a negligeable reduction in the length of the combustion-to-detonation path.
A device bearing the closest resemblance to one described in the present specification is represented in a barrel of an apparatus for applying coatings by gas detonation (cf., A. I. Zverev, et al. "Detonatsionnoe napylenie pokrytii", 1979, the Sudostroenie Publishers, Leningrad, page 172) comprising an arrangement for initiating an explosive mixture, and a detonation chamber with through holes spaced equidistantly about the periphery of its cross section.
After the barrel is filled with the explosive mixture and the gas passages are sealed the mixture is fired at the closed end of the barrel. In this apparatus the flame propagates through the holes to the detonation chamber, and then to the barrel. Such an arrangement aims at reducing the combustion-to-detonation path through more uniform firing of the mixture by transforming the initial ignition center into a plurality of ignition centers arising at the barriers between the holes. These barriers, similar to the Schelkin coil, act as obstacles in the path of propagation of the flame and through additionally agitating the flow act to reduce the length of the combustion-to-detonation path.
However, the use of the aforedescribed construction when initiating detonation in mixtures of a substantial combustion-to-detonation path also results in negligeable reduction in this length.
Initiating detonation by the Schelkin coil has similarities with the process of propagation of stationary detonation in the gas a mixture characterized by the presence of separate ignition centers in the detonation front. These ignition centers bring about local increases in pressure or compression waves moving along the front of the detonation wave across its propagation path in the barrel. These transverse waves collide with each other and with the walls of the tube to cause an increase in the pressure and temperature in the area of collision and ensure stationary propagation of detonation along the barrel.
Investigation into a stationary detonation in a tube with a smoked wall shows a characteristic network of traces with the size of each cell of such network determined by the composition of the explosive gaseous mixture and the initial pressure of this mixture in the barrel. The size of cell in the front of stationary detonation is a major characteristic of the process, and is determined experimentally.